In mobile communication systems, AGC (automatic gain control) is generally performed when radio waves are received. An amplifier used to amplify the amplitude of received signals is contained in a communication apparatus; however, if the power of the received signals (received power) is too large, the amplifier becomes saturated, and distortion appears in the waveform. Accordingly, in mobile communication systems, the gain (amplification factor) of the amplifier is controlled by AGC, so that the amplified received power does not exceed the saturation power of the amplifier (i.e., the threshold power at which the amplifier becomes saturated).
Furthermore, an AGC in which the distribution of the gain of two stages of amplifiers (a low-noise amplifier and an intermediate-frequency amplifier) is determined on the basis of the modulation scheme of the received signals is disclosed in Japanese Laid-Open Patent Application No. 2003-204364.